At the height of the Cold War, British military planners contemplated a weapon that sounds more like the plot of a darkly comic science-fiction movie than a genuine government project. Codenamed Project Blue Peacock, it was a plan to bury enormous nuclear land mines in West Germany in preparation for a possible Soviet invasion. And, remarkably, engineers considered using live chickens to keep the bombs warm.

The project emerged from a very real military problem. During the 1950s, NATO planners feared that Soviet and Warsaw Pact forces could overwhelm Western defenses and drive rapidly across the North German Plain. Britain therefore investigated the possibility of leaving behind nuclear devices that could destroy important installations and make territory unusable to an advancing enemy. The proposed targets included railway junctions, canals, oil refineries, industrial facilities and other infrastructure.

Blue Peacock was to be an enormous device, weighing roughly seven tons and having a nuclear yield of approximately 10 kilotons. It was designed to be buried or otherwise concealed and could be detonated in several ways. One option was a command signal transmitted through a wire from as far as three miles away. Another was an eight-day timer, allowing British forces to withdraw before the weapon exploded. The device also incorporated anti-tampering mechanisms intended to trigger an explosion if someone attempted to move it or interfered with its pressurized casing.

There was, however, a distinctly British complication: winter.

The engineers were concerned that the freezing temperatures of northern Germany could make the weapon’s electronic and mechanical components inoperable before the eight-day period had elapsed. Various solutions were considered, including insulation. But one proposal was considerably more unusual: put live chickens inside the weapon’s casing.

The idea was surprisingly straightforward. Chickens generate considerable body heat, and the engineers calculated that several birds could provide enough warmth to keep the weapon’s internal components above their minimum operating temperature. The birds would be supplied with food and water and would theoretically survive for approximately the required eight days. A 1957 document even discussed chickens as a possible source of roughly 1,000 British thermal units of heat per bird per day.

When details of Blue Peacock were eventually released, the chicken proposal was initially so absurd that many people assumed the British government had engineered an elaborate April Fool’s joke. There was good reason for the confusion: the relevant documents were declassified on April 1, 2004. The National Archives, however, confirmed that the proposal was entirely genuine.

Behind the amusing chicken story was a much more sobering reality. Blue Peacock was not intended merely to destroy Soviet tanks. The enormous explosion would have created substantial radioactive contamination, deliberately denying the territory to an occupying force. In other words, Britain was contemplating the nuclear destruction—and subsequent contamination—of portions of the very country it was supposedly trying to defend. That created enormous political and military complications, particularly because the proposed weapons would have been placed on the territory of Britain’s West German ally.

By 1957, the British Army had gone far enough to order ten Blue Peacock devices for potential deployment in Germany. Their presence would have been concealed under the cover story that they were “atomic power units” intended for troops in the field. The sheer size of the weapons even created practical difficulties during development and testing. A prototype casing was tested at a flooded gravel pit near Sevenoaks, Kent, under the explanation that an insulated container was being evaluated.

Ultimately, common sense—and concerns about the consequences of nuclear warfare—prevailed. By early 1958, officials had concluded that the weapons were too large, posed an unacceptable fallout hazard and presented serious political problems. Pre-positioning nuclear weapons in an allied country during peacetime was particularly troublesome. In February 1958, the Ministry of Defence’s weapons policy committee decided that Project Blue Peacock should be abandoned.

No nuclear chicken ever went to war. But Blue Peacock remains one of the Cold War’s strangest reminders of just how far military planners were prepared to go when contemplating a possible Soviet invasion. Beneath the comedy of the chicken proposal was a frighteningly serious calculation: if Western Europe fell, perhaps a radioactive wasteland would be preferable to letting the enemy occupy it.

The chickens, thankfully, never had to find out.